The present invention relates to a magnetic coil actuator, and particularly relates a lens tracking or focusing driving coil appliance in a CD (compact disc) or DVD (digital versatile disc) driver.
It is known in the art to use a magnetic coil actuator for driving a high precision device, such as a magnetic pickup head in a hard disc driver for tracking the disc tracks, or an optical pickup head in an optical disc driver for focusing the data pits. FIGS. 1A and 1B illustrate a coil driving device of the prior art. It includes mainly a magnet 10, a coil 11 and a yoke 12. The magnetic field of the permanent magnet 10 is illustrated as circular magnetic lines in FIG. 1B. Only a part of the coil 11 is disposed which is charged with to work with the magnetic field of the permanent magnet 10 when a controlling current is charged into the coil 11. However, since the remaining portion of the coil 11 is not disposed aligned with the magnetic field of the magnet 10, the utilitation efficiently of the magnet 10 to the coil 11 is rather low and wasteful.
It is especially true for today""s high reading speed optical disc drivers that the need for accurate tracking and focusing operations requires higher outputs from the coil actuators. Otherwise the tracking or focusing cannot timely respond to the vibration of the disc.
This problem has been recognized by the inventors of the present invention that. The coil actuators of the prior art do not fully utilize the capacity of the coil and do not meet the requirements of high speed optical disc applications.
Accordingly, the primary object of the present invention is to improve the output of a magnetic coil actuator but not to increase the volume of the coil.
A second object of the present invention is to improve the coil actuator of a tracking dervomechanism used in an optical pickup head, and to meet the requirements of higher speed optical disc applications.
A further object of the present invention is to improve the coil actuator, of a focusing servo in an optical pickup head.
A coil actuator according to the present invention uses a flexible magnetic coil whose shape is adjusted to correspond to (i.e., be aligned with) the magnetic field of a static magnet. The coil is suitably bent to have its two diametric sections falling into the magnetic lines of a magnet, so as to maximize the utilization efficiency of the coil relative to the magnetic field. Therefore, the coil actuator maintains the original volume and the same power consumption, but provides a higher output.